1. Field of the Invention
This invention relates to an improvement in the process for resolving the reaction mixture that is formed in preparing propylene oxide and tertiary butyl alcohol by reacting propylene with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of a soluble molybdenum catalyst.
The epoxidation reaction mixture that is formed when propylene is reacted with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of a soluble molybdenum peroxidation catalyst will normally comprise unreacted propylene, propylene oxide, unreacted tertiary butyl hydroperoxide, the soluble molybdenum catalyst and impurities, including C.sub.1 to C.sub.4 lower aliphatic carboxylic acids. The reaction mixture is usually separated by distillation into a plurality of fractions including a recycle propylene fraction, a propylene oxide product fraction, a tertiary butyl alcohol product fraction and a heavy liquid distillation fraction containing tertiary butyl alcohol, unreacted tertiary butyl hydroperoxide and impurities, including subtantially all of the dissolved molybdenum catalyst and a portion of the lower aliphatic carboxylic acids impurities.
In accordance with the present invention about 5 to about 10 wt. % of an aliphatic alcohol containing 1 to 3 carbon atoms is added to the heavy liquid distillation fraction.
The resultant mixture is charged to a falling film evaporator and separated therein, under evaporator operating conditions including a temperature within the range of about 20.degree. to about 150.degree. C. and a pressure of about 1 to about 200 mm Hg., into an overhead vaporized fraction comprising substantially all of the aliphatic alcohol and from about 80 to about 95 wt. % of the heavy distillation fraction charged to the falling film evaporator. The overhead fraction will comprise from about 5 to about 10 wt. % of aliphatic alcohol, from about 60 to 90 wt. % of tertiary butyl alcohol, from about 1 to about 20 wt. % of tertiary butyl hydroperoxide and from about 3 to about 15 wt. % of impurities, including at least some of the lower C.sub.1 -C.sub.4 carboxylic acid impurities.
The practice of the present invention will also provide a clear liquid residue fraction comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and impurities, including substantially all of the molybdenum contained in the heavy liquid fraction.
The overhead vaporized fraction is charged to a distillation zone and separated into a lighter aliphatic alcohol distillate fraction and a heavier distillation fraction containing the other components of the overhead vaporized fraction including the tertiary butyl alcohol, the tertiary butyl hydroperoxide and the impurities. The aliphatic alcohol fraction may be recycled to the falling film evaporator as at least a portion of the lower aliphatic alcohol component of the feed mixture, if desired.